Don't use plain C-Arrays (QString keyStorage [20]), rather use a QStringList here. Your program has serious issues, for example, it will crash when the file contains more than 20 lines.

Your output code accesses indices 0 to 20, but your array only has 0 to 19 indices. So this is a time bomb, too. Another argument not to use C-Arrays if you don't know that you absolutely need them (e.g. for high performance computing).

Style hint: Don't mix naming conventions. Either "keyStorage" and "fileName" or "key_storage" and "file_name". Since working in a Qt environment, you should even prefer the first (called camelCase) style. But in any case, don't mix!